This invention relates in general to certain new and useful improvements in analysis of boundary movement of a dynamically movable structure or portrayed dynamic motion of said structure, and, more particularly, to the analysis of body tissue or a series of sequential images of the body tissue. More specifically, the present invention involves the analysis of video fluoroscopic images to provide a noninvasive means for detection and functional evaluation of clinical ischemic heart disease by a technique termed photokymography.
The photokymograph, often referred to as a "PKG", may be used to obtain both quantitative and/or qualitative records, not only of cardiac movement, such as sequential ventricular wall motion, but also of hemodynamic parameters such as instantaneous volumes, stroke volumes and ejection fractions. The photokymograph is applicable to any system producing a moving cardiac image, such as cineangiography, videofluoroscopy, two-dimensional ultrasonography and gated nuclear blood pool imaging. The photokymograph is directly able to detect and measure the linear motion of cardiac valves and also provide planimetric measurement and analysis of parameters such as ventricular volume, stroke volume, and ejection fraction.
In recent years, the increasing death rate in the population as a whole from cardiovascular disease has brought about a great increase in development of cardiovascular diagnostic equipment and techniques. One of the techniques which is used to measure cardiac output is angiography where a dye is injected into the heart by means of a catheter and the passage of the dye throughout the circulatory system is measured by colorimetric examination of the blood.
This latter technique is quite accurate and is the standard against which other diagnostic systems are measured. However, there is a significant risk to the patient with mortality/morbidity rates as high as four percent reported. Another method in current clinical use for measuring cardiac motion relies upon a radiopaque substance which is introduced into the heart by similar means and the cardiac motion is followed by roetgenography. The patient risk with this technique is less than dye injection because smaller volumes of foreign material are introduced. Measurement of stroke volume and other volumetric quantities has not been practical in most cases due to the complexity thereof.
More recent improvements in X-ray equipment and improved measurement techniques relied upon the substitution of an image intensified tube for the traditional film or fluoroscopic screen. The image obtained on the image intensified tube is then examined by television techniques which are very sensitive to low radiation levels. These improvements have made possible a great reduction in the exposure of the patient to potentially harmful radiation.
More recently there has been a surge in the development of sonar related techniques wherein a beam of ultra-sound is aimed through the area to be examined and the resultant echoes, after computer treatment, have been used to form a picture of the heart or other internal organs of a living human patient on a television screen. One further imaging system involving autoradiography has been developed to provide similar, photo evaluation of cardiac activity. Autoradiography is used in such imaging by injecting a radioactive material, such as technetium, into the blood stream and capturing the resulting pattern of gamma ray radiation from the patient, by a gamma camera including a scintillation crystal and photomultiplier array. After electronic analysis and computer data reduction, the resulting picture can be displayed upon the face of a television screen. The random nature of the radiation events which comprise the elements of the image requires that the image be constructed over a significant time period. The image quality is a direct function of time for a given patient exposure to the radiation. This technique precludes the use of such systems to produce a real time or single beat cardiac measurement.
The images formed by these methods provide a large amount of diagnostic data to the cardiologist by direct viewing. However, precise measure of the motion of the heart as a whole, or portions thereof, can only be performed indirectly. One such method which may be used with a filmed examination of the X-ray image, or "cineangiography", has been to directly measure the image projected onto a translucent screen with dividers or the like, on a frame-by-frame basis. This technique is costly and slow and because it cannot be performed in real time and oftentimes results in poor or incomplete measurements, requiring the patient to undergo a second examination. A second method which is generally only applicable to television type images is called videotracking or "radarkymography". In this technique, the televised fluoroscopic images of a beating heart are used in conjunction with complex and specialized electronic equipment to detect the epicardial ventricular boundary. A voltage proportional to the instantaneous position of the ventricular boundary is generated, and after processing, is transmitted to a strip chart recorder for print-out. This technique is costly and complex. Further, this technique is limited by the nature of the image processing of the video images, due to the fact that the motion to be measured must lie perpendicular to the vertical axis of the video display tube and substantially parallel to the raster lines in the video display tube. Any angular difference between the desired perpendicularity will result in an induced measurement error from geometric causes. The fact that the normal motion of the heart caused by the diaphragm and the rotational component of the systolic contraction is present limits the accuracy which can be realized by this technique. The technique is further limited by an inherent time lag of from forty to fifty milliseconds which produces a significant reduction in high frequency response.
Still another method in common use is "videodensitometry". In this method an area controllable by the operator of the image is brightened by electronic means. This brightened area which constitutes a data "window" is placed over the area of interest so that the window is divided by the image into a bright and dark area which is the boundary of interest. Motion of the boundary will then alter the bright to dark area ratio and produce the requisite data signal. This technique, like videotracking, is limited to video images and suffers from cost, complexity and insensitivity to overall contrast changes such as those which occur during the washout of the contrast medium. Additionally, the control of the "window" position requires a high degree of dexterity and skill on the part of the operator who must hold the window in exact geometric relationship with the movement of the portion of the image to be scanned.